What to wear to a wedding in the fall?

Me and My family Are going to a wedding in Mid-October. the wedding is in Pittsburgh PA. I live Just outside of Orlando FL so i have no idea what the weather is like. the wedding is going to be outside, during the day, on a ferryboat.(: I have no idea what to wear :/ I'm a 13 year old girl. i have dirty blonde hair and tanned skin. my style is more rocker/scene. im fairly skinny and kind of tall. should i wear like a long or short dress and what kind of shoes, jewelry, hair & makeup. thanks in advance(: